|That would be 127.0.0.1 which is the tcp/ip loopback address|
Just to add to what wanderer said about the loopback.
On the DC (domain controller) when it was promoted DNS should have been setup automatically. All domain clients have to connect to the DC and it's DNS in order to authenticate. To ensure clients connect to the DC, you have to provide them with a DNS address (usually within the DHCP settings). Since 127.0.0.1 is a loopback address, you can't supply that one to clients as their DNS IP.
So, you will need to know the LAN address of your DC and ensure your DHCP settings have the DNS address as being the LAN IP of the DC.
One a Cisco router with a Motorola moden. The modem plugged into the router and the workstations (using XP) plugged into the router. Works first time. Second a Netgear modem/router which of course works. and thirdly a netgear switch with a Telstra BigPond modem. The modem is plugged into the Netgear switch and the workstations are plugged into the switch and everything works.
Your setup is a little confusing and seems complex. Is there a particular reason for the multiple routers like separate subnets; or multiple, separate, internet connections?
If you could give a little more detail on how everything is connected physically this might help us avoid giving you bad advice.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.